Plots of USRP decimation woes: input is GMSK waveform @ ~30ksym/sec, BT = 0.35, no noise added using decimation rate of 16: http://img339.imageshack.us/img339/4467/d16cz9.jpg top plot is complex baseband, bottom plot is amplitude of top plot some amplitude variations noticeable, but fairly minor.
using decimation rate of 256: http://img256.imageshack.us/img256/2850/d256qh2.jpg heavy amplitude variations. zoomed in version of previous plots: http://img490.imageshack.us/img490/6528/d256zoomedku7.jpg Still confused as to what is going on here... Plots showing effects of carrier discrepancy between tx and rx on GMSK demodulation: These are plots of the output of the fmdemod block (and of the input to the M&M clock recovery block). Residual carrier manifests as DC offset after fmdemod (look at y-axis): http://img89.imageshack.us/img89/1116/fmdemoduntunedri8.jpg sending input like this into the clock recovery block -> lots of bit errors, especially when noise is added. After manually tweaking tx carrier freq by a few kHz: http://img152.imageshack.us/img152/281/fmdemodtunedwc2.jpg much better, -> 0 bit errors. So, that's the motivation for wanting carrier tracking. I think Eric's right that there's a solution involving filters that doesn't require me to leave python-land, but I'm still a bit confused as to how to leverage the IIR block.
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